Heat-treatment of hardenable metallic articles



Oct. 30, 1945. I H. E. soMEs 2,388,2

HEAT TREATMENT OF HARDENABLE METALLIC ARTICLES Filed Aug. 21, 1945' l N VEN TOR fiowardE. Games ATTORNEY Patented Och 30,1945

HEAT-TREATMENT F HARDENABLE METALLIC ARTICLES Howard E. Somes, Detroit, Mich, assignor to Budd Induction Heating, Inc., Philadelphia, Pa., a corporation of Michigan Application August 21,1943, Serial No. 499,538 6 Claims. (Cl. lis -lil) This invention relates to the heat treatment of h'ardenable metallic articles and particularly articles of such irregularly shaped surface contour as has heretofore rendered the satisfactory hardening thereof in all cases diflicult and in most cases impossible. I

One example of an article having such a sur- I face is an airplane propeller hub which is usually provided with a plurality of radial, blade sockets having groove, inner walls of such sinuous or irregular conformation as has heretofore rendered it extremely dificult if not impossible to control accurately the depth to which the material of the sockets can be hardened beneath the irregular face. Because of the variations in the heat conductivity of the different parts of the article beneath the irregular surface, resulting from the variations in the mass of such parts, if the surface was heated sufiiciently to bring the bottom of the grooves, or the like, to a hardening temperature the entire socket, wall was usually heated through, especially at the thinner parts beneath the grooves. This resulted in the formation of cracks or other defects upon quenching. 0n the other hand, the application of a lesser of which is shown for the purposes of illustration in the accompanying drawing in which:

Fig. 1 is a partial sectional view of an airplane propeller hub showing a blade socket having an irregular surface exemplifying one form of surface which can be successfully hardened by the present method. This figure also shows one form of an apparatus which can be employed in carrying out the present method, and

Fig. 2 is a sectional view of the hub taken at right angles of Fig. 1 illustrating the final quenching operation.

Although, for the purposes of disclosure, the

present invention is described in connection with the hardening of an inner socket wall II in the blade socket ii of a propeller hub l3, it will be apparent that the utility of the present method is not limited to any specific article, but is equally adapted to the hardening of other articles. In the case of the illustrated embodiment the sockets i 2, usually three in number, areformed with relamount of heat usually failed to raise the material at the bottom of the grooves to the required critical temperature, so that only the highpoints of the irregular surface were hardened.

An object of this invention is to provide an improved method of heat treating articles oi uneven or irregular shape for hardening purposes. A further object is to provide a method of heat treating, a metallic article having a surface rem dererl irregular by a plurality of relatively deep grooves, or the like, of such character that variations in the heat conductivity of the different parts of the article beneath the surface, resulting from variations in the relative mass of such parts, is overcome and its interference with the desired heat treatment is substantially nullified. A still further object is to provide a method of hardening a sinuous orgrooved surface on a bo y member of variable cross-section in which the depth of heating to hardening temperature can be accurately controlled and made effective to the desired depth beneath all parts of thasurface, while the balance of the material, regardless of its. mass distribution, is retained at a temperature well below the critical, thus providing a smoothly contoured zone or line of demarcation between the hardened and unhardened layers.

These and other objects which will be apparent from the following description are accomplished in the present invention, one embodiment atively deep grooves it which give the inner socket wall a sinuous contour of constantly varying diameter. At the same time,.the thickness of metal forming the socket wall varies from one end of the socket to the other, due in part to the sinuous conformation of the inner wall and due also to the shaping of the outer wall which may or may not be tapered, particularly near the outer end it of the socket. It will be apparent that the "heat conducting capacity of the socket wall varies from one portion to another, due to the varying mass distribution of material in the wall.

In the present invention, hardening of the grooved socket wall for a determinate depth beneath the bottoms of the grooves, such that a smoothly contoured zone of demarcation will be.

obtained longitudinally of the socket wall between the unhardened and hardened areas, is accomplished by generating a hardening temperature within a surface layer of determinate depth so quickly that the temperature of the surface layer is raised to a hardening point before the heat can drift in any substantial degree by conduction into the surrounding, unheated area. Wherever the socket wall has relatively thin sections of material such, for example, as the sections it beneath the bottoms of thegrooves l4, particularly near the open end of the socket, the generation of heat in the inner surface tends to heat the wall entirely through to the outer face thereof. In order to compensate for the smaller mass of metal at such points, to prevent the heat reaching the outer wall and to provide a smoothly contoured zone of demarcation between the hardfrequency,

ened and unhardened areas of the finished socket,

the present invention includes the step of maintaining the temperature of the outer layer well below the critical. For this purpose a quenching medium is applied to the outer face of .the socket during at least a part of the heating period. This primary external quench is augmented toward the end of the heating period by a secondary external quench which is also applied to the outer surface of the socket but nearer the base thereof than the primary quench. At the end of the heating operation, the inner, heated surface is quenched by impinging a quenching medium directly thereon. 4

In my copending application, Serial No. 476,991, filed February 24, 1943, there is disclosed one embodiment of a heat treating apparatus which can be employed in carrying out the present invention. In the present drawing, there is shown only suchparts of the machine as are needed to obtain a complete understanding of the present method.

The inner socket surface is preferably heated by. electromagnetic induction. For'this purpose an induction heating head 20, having a water cooled, tubular induction heating coil 2| is mounted on an annular laminated core 22 at the lower end of a hollow supporting mandrel 23. A quench tube 24 having a quench nozzle 25 at the lower end thereof is'positioned within the hollow mandrel 23 and. is' movable relatively thereto. Both heating head and quench tubes are movable into and out of operative position with the hub socket. An external quench head 29 is adapted to surround the socket during treatment. A primary quench channel 3| in the head leads to an annular primary quench nozzle 32 and a secondary quench passage 33 leads to an annular secondary quench nozzle 34. The primary quench nozzle is located so as to direct a continuous annular stream of quenching fluid against the entire circumference of the outer surface of the socket wall adjacent the end thereof.

The secondary quench nozzle is adapted to direct.

a second annular sheet of quenching fluid around the entire circumference of the socket wall at a point about midway thereof. The quench head is formed with an annular skirt 36 extending downwardlly below the primary nozzle 32 for the purpose of providing a confining path for the primary quenching mild to compel it to follow the wallsurface of the socket and keep it in contact therewith. At the presenttime the primary and secondary quenching fluids are preferably liquid, such as water, while the interior quenching fluid which is impinged upon the by directinga stream of quenching fluid, such as water, through the primary quenching nozzle 32 so that an annular, continuous sheet of water is caused to impinge upon the outer shoulder 31 at the upper end of the socket and this quenching fluid is directed downwardly along the outer wall by the skirt 36 which maintains it in heat extracting contact therewith. A suitable gasket 38 is employed between the quench head and the end of the socket to prevent quenching fluid reaching the interior of the bore during the heating operation. Application of this primary quench during the heating period prevents the heat generated in the inner wall from flowing by conduction through the relatively thin sections beneath the bottoms of the grooves It and reaching the outer surface and, thus, confines the hardening temperature to the inner layer of determinate depth. At the same time, the high power, high frequency inducing currents are such as to assure generation of a hardening temperature throughout the inner wall surface beneath all parts thereof including the bottoms of the For example, I have accomplished highly satisheated surface by the nozzle 25 is preferably a gas or air.

. In operation, the hub is mounted in a suitable fixture (not shown) with the socket bore to be hardened in position to receive the heating coil M, as shown in Fig. 1. High power, high electromagnetic inducing current passes through the coil, inducing heating currents in the surface of the socket of such intensity and character that the inner surface of the socket bore is quickly raised to a hardening temperature. In order to confine the heating effect to a layer of predetermined .thickness beneath the grooves I4, and to provide a relatively smoothly contoured zone of demarcation 4] between the hardened and unhardened layers, the primary quench is applied to the outer surface of the socket, during the heating operation while the heating current is supplied to the coil H,

seconds.

factory results by heating for a period of 17 /2 After fifteen seconds of heat, the primary quench is applied. At "the end of 17%, seconds the heat is cut off. Thereupon the heat head is removed from the socket and the secondary quench, preferably water, is applied by directing the water through the nozzle 34 .to impinge against the outer face of the socket, simultaneously with the primary quench through the nozzle 32. Simultaneously, quenching medium is directed against the inner heated surface by the inner nozzle 25, and I now prefer to employ air as the inner quenching medium. After fifty seconds of quench with both primary and secondary external quench and the internal quench combined.

- the operation is complete.

It will be apparent that the present invention provides a hardening treatment which includes what may be termed a differential quenching operation, to counter the effect of the variable heat conductivity in articles of varying crosssection, and results in hardening a surface of irregular conformation while providing a smoothly contoured zone of demarcation between the hardened and unharde'ned areas. The primary quench provides a localized external quench over the part of the blade socket wall which has less backingmaterial to absorb the heat which may tend to drift into it by conduction from the heated layer. In one aspect, the primary quench artificially provides the blade socket with a more uniform wall thickness by providing water quenching in those'parts of relatively small crosssection which are lacking in mass. These areas are locally cooled by the primary quench and are thus prevented from being hardened all the way through. Also, a smoothly contoured zone of demarcation is. produced separating the hardened and unhardened layers. The secondary quench functions in the usual manner in conjunction with the internal air quench.

Any desired quenching media can, of course, be employed. With the 'article described, the characteristics of the steel used are such as to render an internal air quench preferable to a water quench. Obviously the invention can be variously modified and adapted within the scope of the appended claims.

What is claimed is: y

1. The method of zone hardening an annular wall hardenable by heating and quenching and havingregions of varying thickness, which consists in inducing annular heating currents in one wall surface to a substantially uniform depth less than the thickness of the region of least thickness, simultaneously extracting heat at such nonuniform rate from the opposite wall surface as regards the regions of greatest and least thickness that the longitudinal and circumferential increments of that :boundary of the zone heated by the induced currents which lies between said surfaces reach hardening temperature simultaneously, and upon attainment of said hardening temperatures discontinuing said heating currents.

2. The methodof zone hardening an annular wall hardenable by heating and quenching and having regions of varying thickness, which con- .sists in inducing annular. heating currents in one intermediate said wall surfaces reach hardening temperatures substantially simultaneously, and

then upon the attainment of said hardeningtemperatures discontinuing said heat currents;-

3. The method of zone hardening an annular than the thickness of the region of least thickness, then, just prior to the zone heated bysaid induced currents reaching hardening temperature directing a cooling medium against the opposite wall surface at'the region of least thickness in a manner such that the longitudinal and circumferential increments of the boundary bethickness at a rate greater than from 'the region of greatest thickness, said rate of heatextracf tion being such that the longitudinal and circumferential inc ements of that boundary of the zone heated by aid induced currents which lies intermediate said wall surfaces reach hardenin temperatures substantially simultaneously, and.

then while continuing the direction of cooling wall hardenable by heating and quenching and 1 ential increments of that boundary of the zone heated by said induced currents which lies intermediate said wall surfaces reach hardening temperatures substantially simultaneously, then upon the attainment of said hardening temperatures discontinuing said heat currents, and then while continuing the extraction of heat directing a quenching medium against said first mentioned wall surface.

a. The method of zone/hardening an annular wall hardenable by heating and, quenching and having regions of v ng thickness, which consists in inducing ular heating currents in one wall surface to a substantially uniform depth less medium against s'aid-opposite wall. surface and while directing 3' additional cooling medium against said opposite wall ,surface adjacent the region of greatest thickness, directing quenching fluid againstsaid first/mentioned wall surface. 6. The method of zone hardening the bore of an annular metallic wall hardenable by heating and quenching and having regions of varying thickness, which consists in inducing annular heating currents in the internal surface of said wall to a depth less than the thickness of the region of lesser thickness to heat the zone to be hardened, and, prior tosaid zone reaching hardening temperature, applying a primary liquid cooling medium to the external surface of said wall at the region of lesser thickness to extract from the metal surrounding said zone conducted heat at a rate faster from said region than from the region of greater thickness, then upon said 

